Process for the preparation of cobalt sulfate salts

Abstract

In a method of preparing a cobalt sulfate salt, a feed solution comprising cobalt sulfate and an aqueous solution of sulfuric acid is prepared; the feed solution is subjected to evaporative crystallization to form a first solution; the first solution is subjected to a first purging and filtration to form a first cobalt sulfate salt; an aqueous solution comprising the first cobalt sulfate salt is subjected to cooling crystallization to form a second solution; the second solution is subjected to a second purging and filtration to form a second cobalt sulfate salt.

Description

Technical Field

[0001] This invention relates to a method for preparing cobalt sulfate. More specifically, this invention relates to a method for preparing cobalt sulfate including a refining process. Background Technology

[0002] In recent years, secondary batteries have been widely used and developed as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops, as well as vehicles such as hybrid electric vehicles and electric vehicles. Lithium-ion batteries, as secondary batteries, have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design; therefore, their development and application are actively pursued.

[0003] The positive electrode active material of the lithium secondary battery can be a lithium metal oxide. The lithium metal oxide may contain cobalt, and may also contain transition metals such as nickel and manganese.

[0004] Because the aforementioned high-cost metals are used in the positive electrode active material, manufacturing the positive electrode material requires more than 20% of the manufacturing cost. Furthermore, with the increasing prominence of environmental issues in recent years, methods for recycling the positive electrode active material are being researched.

[0005] For example, cobalt can be recovered in the form of cobalt sulfate by leaching waste positive electrode active material with strong acid, and the recovered cobalt sulfate can be used to prepare positive electrode active material again.

[0006] However, the recovered cobalt sulfate may contain other transition metals as impurities, such as manganese. Therefore, a process design is needed to obtain high-purity cobalt compounds without excessively reducing the cobalt yield. Summary of the Invention

[0007] Technical problems to be solved

[0008] One technical problem of the present invention relates to a method for preparing cobalt sulfate salts with improved purity and yield.

[0009] Technical solution

[0010] In a method for preparing cobalt sulfate according to an exemplary embodiment, a feed solution comprising cobalt sulfate and an aqueous solution of sulfuric acid is prepared; the feed solution is evaporated and crystallized to form a first solution; the first solution is first purged and filtered to form a first cobalt sulfate; the aqueous solution comprising the first cobalt sulfate is cooled and crystallized to form a second solution; the second solution is second purged and filtered to form a second cobalt sulfate.

[0011] In some implementations, the temperature for the evaporation crystallization can be 60-80°C.

[0012] In some implementations, the temperature for cooling crystallization can be 10-20°C.

[0013] In some embodiments, the proportion of the first solution by weight of the solution removed by the first purging may be less than 5% by weight.

[0014] In some embodiments, the proportion of the solution removed by the first purge in the weight of the first solution can be 1-5% by weight.

[0015] In some embodiments, the proportion of the solution removed by the second purge in the second solution can be 5-20% by weight.

[0016] In some embodiments, the proportion of the solution removed by the second purge in the second solution can be 5-10% by weight.

[0017] In some embodiments, the proportion of the second solution by weight of the solution removed by the second purging may be greater than or equal to the proportion of the first solution by weight of the solution removed by the first purging.

[0018] In some embodiments, the feed solution may further contain manganese impurities.

[0019] In some embodiments, the amount of manganese impurities removed during the cooling crystallization may be greater than the amount of manganese impurities removed during the evaporation crystallization.

[0020] In some embodiments, the first cobalt sulfate salt may comprise cobalt sulfate monohydrate (CoSO4·H2O), and the second cobalt sulfate salt may comprise cobalt sulfate heptahydrate (CoSO4·7H2O).

[0021] In some embodiments, the steps of performing the first purging and filtration on the first solution or the second purging and filtration on the second solution may include recycling the liquid phase separated by filtration back into the feed solution.

[0022] Beneficial effects

[0023] According to the above exemplary implementation, cobalt sulfate salt can be obtained with high purity by sequentially evaporating and cooling the feed solution containing cobalt sulfate for crystallization.

[0024] According to an exemplary embodiment, by performing a first purging between the evaporation crystallization and the cooling crystallization, the concentration of sulfuric acid in the solution can be reduced, thereby promoting the crystallization of cobalt sulfate. Furthermore, by performing a second purging after the cooling crystallization, the amount of liquid phase can be reduced, thus reducing the amount of residual manganese contained in the feed solution.

[0025] According to an exemplary implementation, by adjusting the purging amounts of the first purging and the second purging, the yield and purity of the recovered cobalt sulfate can be improved simultaneously. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart illustrating a method for preparing cobalt sulfate according to an exemplary embodiment. Detailed Implementation

[0027] An embodiment of the present invention provides, for example, a method for preparing cobalt sulfate from the positive electrode active material of a lithium secondary battery with high purity and high yield.

[0028] However, embodiments of the present invention are not limited to processes for recycling from lithium secondary batteries, but can be applied to various preparation processes and product processes accompanying the refining process of cobalt sulfate.

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0030] Figure 1 This is a schematic flowchart illustrating a method for preparing cobalt sulfate according to an exemplary embodiment.

[0031] Reference Figure 1 A feed solution containing cobalt can be prepared (e.g., process S10).

[0032] The feed solution may contain cobalt sulfate (CoSO4). In some embodiments, cobalt sulfate may be obtained from the positive electrode active material of spent lithium secondary batteries or used lithium secondary batteries.

[0033] For example, the waste positive electrode can be recycled by separating the positive electrode from the waste lithium secondary battery. The waste positive electrode may include a positive electrode current collector (e.g., aluminum (Al)) and a positive electrode active material layer, and the positive electrode active material layer may contain, for example, nickel-cobalt-manganese (NCM)-based lithium transition metal oxides (e.g., Li(NCM)O2).

[0034] The active material layer of the cathode can be separated from the waste cathode to collect the active material mixture, which is then treated with sulfuric acid along with a reducing agent such as hydrogen peroxide (H2O2) to form an active material solution.

[0035] In some embodiments, in order to reduce the residual current collector, conductive material and / or binder components in the active material mixture, further processes such as precipitation, filtration, centrifugation and washing using alkali can be performed.

[0036] By adding a transition metal extractant to the solution of the active substance, nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4) can be formed from Ni, Co, and Mn, respectively, and then collected. For example, the transition metal extractant may contain a phosphate-based compound.

[0037] In some embodiments, the extraction of the transition metal can be carried out while gradually increasing the pH. For example, Mn, Co, and Ni can be extracted sequentially while increasing the pH.

[0038] For example, manganese sulfate (MnSO4), cobalt sulfate (CoSO4), and nickel sulfate (NiSO4) can be extracted sequentially while gradually increasing the pH of the active substance solution.

[0039] A feed solution containing cobalt sulfate collected as described above can be prepared. The feed solution may contain cobalt sulfate contained in an aqueous sulfuric acid solution and may contain unextracted residual manganese sulfate as an impurity. A crystallization process for obtaining high-purity cobalt sulfate can be performed as described below.

[0040] For example, in process S20, the feed solution can be evaporated and crystallized.

[0041] The evaporation crystallization may include a reduced-pressure evaporation process. For example, the evaporation crystallization can be carried out in a temperature range of approximately 60-80°C. Figure 1 As shown, through the evaporation and crystallization, a portion of the water (H2O) can be removed, and a first solution with an increased concentration of cobalt sulfate can be prepared.

[0042] Subsequently, for example, in processes S30 and S40, a first cobalt sulfate salt can be obtained by a first filtration process of the first solution.

[0043] The first filtration process may include, for example, a solid-liquid phase separation (solid / liquid separation) process using a filter press or centrifugal dehydration process. Through the first filtration process, at least part of the liquid phase can be removed and separated, while the first cobalt sulfate salt of the solid phase can be extracted.

[0044] In some implementations, the liquid phase separated by the first filtration process can be recycled back into the feed solution (e.g., first recycle C1). Therefore, cobalt not recovered through the evaporation crystallization can be recycled, thereby increasing the cobalt recovery rate.

[0045] In some embodiments, the first cobalt sulfate salt may comprise cobalt sulfate monohydrate (CoSO4·H2O).

[0046] According to an exemplary embodiment, the first solution may be subjected to a first purging. In some embodiments, such as Figure 1 As shown, the first purging can be performed simultaneously with the first filtration process.

[0047] The first purging process removes a predetermined portion of the first solution added to the first filtration process. Therefore, the concentration of sulfuric acid can be reduced during the first filtration process, thereby improving the solid / liquid separation efficiency. Consequently, the collection efficiency and yield of the first cobalt sulfate can be increased.

[0048] exist Figure 1 In this document, process S20 and process S30 are separately represented as evaporation crystallization and first filtration, respectively, but process S20 and process S30 can be included together as evaporation crystallization.

[0049] The collected first cobalt sulfate can be further subjected to cooling crystallization, for example, in process S50. For instance, distilled water can be added to the first cobalt sulfate to form an aqueous solution. For optimal dissolution efficiency, the temperature of the distilled water can be approximately 60-80°C. The aqueous solution can then be cooled to approximately 10-20°C to form a second solution.

[0050] Subsequently, for example, in processes S50 and S60, a second cobalt sulfate salt can be obtained by a second filtration process of the cooled second solution.

[0051] The second filtration process may include, for example, a solid-liquid phase separation (solid / liquid separation) process using a filter press or centrifugal dehydration process. Through the second filtration process, the liquid phase of the second solution can be at least partially removed and separated, while the solid phase of the second cobalt sulfate can be extracted.

[0052] In some embodiments, the second cobalt sulfate salt may comprise cobalt sulfate heptahydrate (CoSO4·7H2O).

[0053] In some embodiments, the liquid phase separated by the second filtration process can be recycled back into the feed solution (e.g., second recycling C2). Therefore, the unrecovered cobalt obtained through the cooling crystallization can be recycled, thereby increasing the cobalt recovery rate.

[0054] According to an exemplary embodiment, the second solution can be subjected to a second purging. In some embodiments, such as Figure 1 As shown, the second purging can be performed simultaneously with the second filtration process.

[0055] The second purging removes a predetermined portion of the second solution added to the second filtration process. The second purging also reduces the amount of residual manganese that cannot be separated by the cooling crystallization. Therefore, the efficiency of manganese removal and separation can be improved through the second filtration. Consequently, the purity of the second cobalt sulfate collected in step S70 can be increased.

[0056] exist Figure 1 In this context, process S50 and process S60 are separately represented as cooling crystallization and second filtration, but process S50 and process S60 can be included together as cooling crystallization.

[0057] In some implementations, the purge rate in the second purge may be greater than or equal to the purge rate in the first purge.

[0058] In one embodiment, the proportion of the solution removed in the first purge (the first purge rate) in the weight of the first solution can be about 5% by weight or less, preferably about 1-5% by weight. Within the range of the above-mentioned first purge rate, the separation efficiency of the first cobalt sulfate can be improved, while the overall yield is not excessively reduced.

[0059] In one embodiment, the proportion of the solution removed in the second purging (the second purging rate) in the weight of the second solution can be about 5-20% by weight, preferably about 5-15% by weight, and more preferably about 5-10% by weight. Within the range of the above-mentioned second purging rate, the total yield of cobalt sulfate can be prevented from decreasing excessively, while manganese impurities can be sufficiently removed.

[0060] As described above, in one embodiment, the second purging rate can be adjusted to be greater than or equal to the first purging rate. Therefore, the crystallization efficiency of total sulfate can be relatively improved during the evaporative crystallization, while the removal efficiency of manganese impurities can be improved during the cooling crystallization.

[0061] For example, the liquid phase can be separated from the feed solution through the evaporation crystallization, while the formation efficiency of solid salt can be improved by the first purging. The first solution formed after the evaporation crystallization may contain a relatively large amount of manganese impurities, which can be removed by the cooling crystallization.

[0062] Therefore, the amount of manganese removed by the cooling crystallization can be greater than the amount removed by the evaporation crystallization. By combining the cooling crystallization with the second purging, the removal efficiency of manganese impurities can be further improved, and high-purity cobalt sulfate can be obtained.

[0063] The following are specific experimental examples to help understand the present invention. However, these are only for illustrating the present invention and are not intended to limit the scope of the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept, which will be obvious to those skilled in the art, and such modifications and variations also fall within the scope of the claims.

[0064] Example 1

[0065] Use a feed solution containing 800 ppm MnSO4, 5-6% H2SO4 and 3 kg CoSO4.

[0066] The feed solution was subjected to reduced pressure evaporation for 8 hours at 70°C and a pressure of 200-500 mbar to form a first solution. The first solution was then filtered through a vacuum pump while maintaining a first purging rate of 5% by weight to obtain cobalt sulfate monohydrate (CoSO4·H2O) as the first cobalt sulfate salt.

[0067] 0.6 kg of distilled water (70 °C) was added to the obtained first cobalt sulfate salt, and the solution was cooled at 15 °C for 2 hours to form a second solution. The second solution was filtered through a vacuum pump while maintaining a second purging rate of 5 wt% to obtain cobalt sulfate heptahydrate (CoSO4·7H2O) as the second cobalt sulfate salt.

[0068] Examples 2 to 4

[0069] Except for adjusting the first and second purging rates as shown in Table 1, cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained using the same process as in Example 1.

[0070] Comparative Example 1

[0071] Cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained by the same process as in Example 1, except that a second purging was not performed during cooling crystallization.

[0072] Comparative Example 2

[0073] Cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained by the same process as in Example 1, except that the first purging was not performed during evaporation and crystallization.

[0074] For the products obtained in the above examples and comparative examples, the amount of cobalt recovered relative to the feed solution (recovery rate (%)), the manganese content, and the purity of the cobalt sulfate salt were measured. Purity was calculated as the weight of cobalt sulfate heptahydrate relative to the total weight of the obtained product, the weight of which was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0075] The evaluation results are recorded in Table 1 below.

[0076] [Table 1]

[0077] First purging rate (wt%) 5 5 5 10 5 - Second purging rate (wt%) 5 10 20 5 - 5 Co recovery rate 94.35 91.09 85.18 92.44 97.86 96.34 Mn (ppm) 2984 2638 2183 3032 3472 7020 purity(%) 99.18 99.27 99.40 99.17 99.05 98.07

[0078] Referring to Table 1, according to the embodiments, by combining the first purging and the second purging, the amount of manganese impurities can be reduced, while ensuring a cobalt recovery rate of over 85%.

[0079] In Comparative Example 1 or Comparative Example 2, where the first or second purging was omitted, the amount of residual manganese increased, or the sulfuric acid was not sufficiently removed and thus concentrated, resulting in a decrease in the purity of the cobalt salt.

Claims

1. A method for preparing cobalt sulfate, the method comprising the following steps: Prepare a feed solution containing cobalt sulfate and an aqueous solution of sulfuric acid; The feed solution is evaporated and crystallized to form a first solution; The first solution is subjected to a first purging and filtration to form a first cobalt sulfate salt; The aqueous solution containing the first cobalt sulfate is cooled and crystallized to form a second solution; as well as The second solution is subjected to a second purging and filtration to form a second cobalt sulfate salt. The proportion of the solution removed by the first purging in the first solution is 1-5% by weight. The proportion of the solution removed by the second purging in the second solution is 5-20% by weight.

2. The method for preparing cobalt sulfate according to claim 1, wherein, The evaporation crystallization temperature is 60-80℃.

3. The method for preparing cobalt sulfate according to claim 1, wherein, The cooling crystallization temperature is 10-20℃.

4. The method for preparing cobalt sulfate according to claim 1, wherein, The proportion of the solution removed by the second purging in the second solution is 5-10% by weight.

5. The method for preparing cobalt sulfate according to claim 1, wherein, The proportion of the second solution whose weight is removed by the second purging is greater than or equal to the proportion of the first solution whose weight is removed by the first purging.

6. The method for preparing cobalt sulfate according to claim 1, wherein, The feed solution further contains manganese impurities.

7. The method for preparing cobalt sulfate according to claim 6, wherein, The amount of manganese impurities removed during the cooling crystallization is greater than the amount of manganese impurities removed during the evaporation crystallization.

8. The method for preparing cobalt sulfate according to claim 1, wherein, The first cobalt sulfate salt contains cobalt sulfate monohydrate (CoSO4·H2O), and the second cobalt sulfate salt contains cobalt sulfate heptahydrate (CoSO4·7H2O).

9. The method for preparing cobalt sulfate according to claim 1, wherein, The step of performing the first purging and filtration on the first solution or the step of performing the second purging and filtration on the second solution includes recycling the liquid phase separated by filtration back into the feed solution.

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